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Summary: Ctors | Methods | Protected Methods | Inherited Methods

# FutureTask

`public class FutureTask`
`extends Object` `implements RunnableFuture<V>`

java.lang.Object
↳ | java.util.concurrent.FutureTask<V>

A cancellable asynchronous computation. This class provides a base implementation of `Future`, with methods to start and cancel a computation, query to see if the computation is complete, and retrieve the result of the computation. The result can only be retrieved when the computation has completed; the `get` methods will block if the computation has not yet completed. Once the computation has completed, the computation cannot be restarted or cancelled (unless the computation is invoked using `runAndReset()`).

A `FutureTask` can be used to wrap a `Callable` or `Runnable` object. Because `FutureTask` implements `Runnable`, a `FutureTask` can be submitted to an `Executor` for execution.

In addition to serving as a standalone class, this class provides `protected` functionality that may be useful when creating customized task classes.

## Summary

### Public constructors
`FutureTask(Callable<V> callable)` Creates a `FutureTask` that will, upon running, execute the given `Callable`.
`FutureTask(Runnable runnable, V result)` Creates a `FutureTask` that will, upon running, execute the given `Runnable`, and arrange that `get` will return the given result on successful completion.

### Public methods
`boolean` | `cancel(boolean mayInterruptIfRunning)` Attempts to cancel execution of this task.
`V` | `get(long timeout, TimeUnit unit)` Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
`V` | `get()` Waits if necessary for the computation to complete, and then retrieves its result.
`boolean` | `isCancelled()` Returns `true` if this task was cancelled before it completed normally.
`boolean` | `isDone()` Returns `true` if this task completed.
`void` | `run()` Sets this Future to the result of its computation unless it has been cancelled.

### Protected methods
`void` | `done()` Protected method invoked when this task transitions to state `isDone` (whether normally or via cancellation).
`boolean` | `runAndReset()` Executes the computation without setting its result, and then resets this future to initial state, failing to do so if the computation encounters an exception or is cancelled.
`void` | `set(V v)` Sets the result of this future to the given value unless this future has already been set or has been cancelled.
`void` | `setException(Throwable t)` Causes this future to report an `ExecutionException` with the given throwable as its cause, unless this future has already been set or has been cancelled.

### Inherited methods
From class `java.lang.Object`
`Object` | `clone()` Creates and returns a copy of this object.
`boolean` | `equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void` | `finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>` | `getClass()` Returns the runtime class of this `Object`.
`int` | `hashCode()` Returns a hash code value for the object.
`final void` | `notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void` | `notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String` | `toString()` Returns a string representation of the object.
`final void` | `wait(long timeout, int nanos)` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
`final void` | `wait(long timeout)` Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
From interface `java.util.concurrent.RunnableFuture`
`abstract void` | `run()` Sets this Future to the result of its computation unless it has been cancelled.
From interface `java.lang.Runnable`
`abstract void` | `run()` When an object implementing interface `Runnable` is used to create a thread, starting the thread causes the object's `run` method to be called in that separately executing thread.
From interface `java.util.concurrent.Future`
`abstract boolean` | `cancel(boolean mayInterruptIfRunning)` Attempts to cancel execution of this task.
`abstract V` | `get(long timeout, TimeUnit unit)` Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.
`abstract V` | `get()` Waits if necessary for the computation to complete, and then retrieves its result.
`abstract boolean` | `isCancelled()` Returns `true` if this task was cancelled before it completed normally.
`abstract boolean` | `isDone()` Returns `true` if this task completed.

## Public constructors

### FutureTask

    public FutureTask (Callable<V> callable)

Creates a `FutureTask` that will, upon running, execute the given `Callable`.

Parameters
`callable` | `Callable`: the callable task

Throws
`NullPointerException` | if the callable is null

### FutureTask

    public FutureTask (Runnable runnable,
                    V result)

Creates a `FutureTask` that will, upon running, execute the given `Runnable`, and arrange that `get` will return the given result on successful completion.

Parameters
`runnable` | `Runnable`: the runnable task
`result` | `V`: the result to return on successful completion. If you don't need a particular result, consider using constructions of the form: `Future<?> f = new FutureTask<Void>(runnable, null)`

Throws
`NullPointerException` | if the runnable is null

## Public methods

### cancel

    public boolean cancel (boolean mayInterruptIfRunning)

Attempts to cancel execution of this task. This attempt will fail if the task has already completed, has already been cancelled, or could not be cancelled for some other reason. If successful, and this task has not started when `cancel` is called, this task should never run. If the task has already started, then the `mayInterruptIfRunning` parameter determines whether the thread executing this task should be interrupted in an attempt to stop the task.

After this method returns, subsequent calls to `isDone()` will always return `true`. Subsequent calls to `isCancelled()` will always return `true` if this method returned `true`.

Parameters
`mayInterruptIfRunning` | `boolean`: `true` if the thread executing this task should be interrupted; otherwise, in-progress tasks are allowed to complete

Returns
`boolean` | `false` if the task could not be cancelled, typically because it has already completed normally; `true` otherwise

### get

    public V get (long timeout,
                    TimeUnit unit)

Waits if necessary for at most the given time for the computation to complete, and then retrieves its result, if available.

Parameters
`timeout` | `long`: the maximum time to wait
`unit` | `TimeUnit`: the time unit of the timeout argument

Returns
`V` | the computed result

Throws
`CancellationException` |
`ExecutionException` |
`InterruptedException` |
`TimeoutException` |

### get

    public V get ()

Waits if necessary for the computation to complete, and then retrieves its result.

Returns
`V` | the computed result

Throws
`CancellationException` |
`ExecutionException` |
`InterruptedException` |

### isCancelled

    public boolean isCancelled ()

Returns `true` if this task was cancelled before it completed normally.

Returns
`boolean` | `true` if this task was cancelled before it completed

### isDone

    public boolean isDone ()

Returns `true` if this task completed. Completion may be due to normal termination, an exception, or cancellation -- in all of these cases, this method will return `true`.

Returns
`boolean` | `true` if this task completed

### run

    public void run ()

Sets this Future to the result of its computation unless it has been cancelled.

## Protected methods

### done

    protected void done ()

Protected method invoked when this task transitions to state `isDone` (whether normally or via cancellation). The default implementation does nothing. Subclasses may override this method to invoke completion callbacks or perform bookkeeping. Note that you can query status inside the implementation of this method to determine whether this task has been cancelled.

### runAndReset

    protected boolean runAndReset ()

Executes the computation without setting its result, and then resets this future to initial state, failing to do so if the computation encounters an exception or is cancelled. This is designed for use with tasks that intrinsically execute more than once.

Returns
`boolean` | `true` if successfully run and reset

### set

    protected void set (V v)

Sets the result of this future to the given value unless this future has already been set or has been cancelled.

This method is invoked internally by the `run()` method upon successful completion of the computation.

Parameters
`v` | `V`: the value

### setException

    protected void setException (Throwable t)

Causes this future to report an `ExecutionException` with the given throwable as its cause, unless this future has already been set or has been cancelled.

This method is invoked internally by the `run()` method upon failure of the computation.

Parameters
`t` | `Throwable`: the cause of failure

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